Which rules should I define for the predicate "not_to_far" of the exercise 1.1 of the book "Simply Logical: Intelligent Reasoning by Example"?

Question

I've just started reading a book about AI. The book is Simply Logical: Intelligent Reasoning by Example. There is a very basic exercise (on page 19 of the pdf, page 5 of the book), but I can't figure it out.

The exercise is

Exercise 1.1. Two stations are 'not too far' if they are on the same or a different line, with at most one station in between. Define rules for the predicate not_too_far.

The only rules I've seen are nearby and connected and don't know how to use this. What I've done so far is this:

not_too_far(X,Y) :- nearby(X,Y)

Answer 1

Your intuition is good. Because "nearby" is only defined with "connected", there could only be 1 station between them. However, it says that the stations are "not_too_far" if at most one station is between them. What about if no stations are between them? If 2 stations are "connected" they should be "not_too_far" as well.

So it should be:

not_too_far(X,Y) :- connected(X,Y) ; nearby(X,Y).

Where ; denotes OR.